I recall going on a 3-day course to a marine officer training camp somewhere in VA. There was a obstacle course which was hard, i.e. you had to swim in cold muddy waters (October time), climb fences, dig trenches etc. 80% of teams finished within the deadline of 4 hours. And then there was a exercise room which the Marine instructors said was designed by CIA. You're locked into a room with some instruments and are given an assignment to be completed under a deadline. The outcome was binary: yes/no. Success rate was like 10%. The odds were so that they can identify the best decile.